Since fiberglass reinforced pipe was introduced, various means have been tried for joining together end-to-end lengths of the pipe, fittings, flanges and adapters. These different means have met with varying degrees of success but none has been completely acceptable. Particular difficulty has been encountered in developing a joint that can be installed quickly and easily in the field when used for repair.
Some such prior means provide a purely mechanical joint between lengths of pipe. The ends of the pipe to be joined have matching threaded joint components. However, because the joint formed is purely mechanical, an 0-ring must be used between the pipe ends to prevent leaking. Thus, this type of coupling cannot be used in services where the materials carried by the pipe could attack the O-ring. This represents a limitation on the use of this type of coupling.
A number of prior means have been used that provide a bonded joint between lengths of pipe. The most common of these is the bell and spigot joint. This joint, as embodied by a female by female coupling has a cylindrical sleeve with an inner wall that tapers outwardly at a slight angle, about 1.degree.45', from the mid point of the coupling toward both ends. To form the joint, the ends of the pipe to be joined must be shaved at their outer walls to have an inward taper toward the ends of the pipe that will match that of the coupling. Adhesive is then spread on the tapered surfaces of the pipe and coupling and the pipe ends inserted into the opposite ends of the coupling. It is very important that the tapers on the pipe and the coupling match closely. Otherwise, air will be trapped in the adhesive and the joint could fail at less than the rated pressure. It is also very important that the tapered surfaces be kept clean to avoid contamination in the joint that could cause it to fail. After assembly, the joint cannot be moved until the adhesive has cured. As embodied by a flange or adapter, this joint would have only one tapered end and accept only one pipe end. Performance characteristics would be identical.
Because of the need for close tolerance shaving, the need to avoid surface contamination, and the sensitivity to movement, the bell and spigot joint does not make a good field repair means. In addition, the integrity of the joint formed by this type of coupling is dependent upon the pipe ends being inserted tightly within the joint component. However, it can be very difficult to control pipe length so that a pipe end can be inserted tightly within a coupling, for example, especially in the repair context. To repair a broken or damaged pipe, a length of the pipe around the broken or damaged spot is cut through and removed. A replacement length of pipe is then joined to the remaining pipe at either end. If the length of this replacement section is too short, it will not fit tightly in the couplings at both ends. Thus, one of the repair joints may fail. It is very common for a replacement section to be short to facilitate positioning the section between the couplings.
Another bonded joint uses a configuration that has a straight socket and spigot arrangement. To form this joint, the ends of the pipe to be joined are shaved to create a squared-off indentation extending around the outer surface of the pipe at the ends of the pipe. Thus, cylindrical lengths having outside diameters less than that of the pipe are provided at the pipe ends. The to- be-bonded joint component has an inside diameter equal to that of the pipe and a bell with inside diameter capable of fitting over the shaved portions on the pipe ends. The inner walls of the bells may slightly taper outwardly toward their respective pipe ends. Adhesive is spread on 20 the inner wall of the bell and on the shaved pipe end and then the pipe end is inserted into the bell. The taper on the bell is provided to allow trapped air to escape from the adhesive when the pipe ends are inserted.
This joint suffers from most of the same problems encountered with the bell and spigot joint. The outer diameter of the pipe ends must be closely matched to the inner diameter of the bells or the joint will not be tight. Air can be trapped in the adhesive. Surface contamination must be avoided. Also, this joint is more sensitive to movement before the adhesive is cured than the bell and spigot joint. Control over pipe length, however, is more accurately measurable with this type of joint. Similar performance is found in straight socket joints not requiring shaving of the pipe end.
A joint has also been developed to form bonded joints that would not be as sensitive to movement before the adhesive has cured. This coupling has a cylindrical sleeve with an inner wall having a series of surfaces that taper outwardly toward both ends. These outwardly tapered surfaces are separated by axially extending surfaces so that the inner wall at each end of this coupling forms an outwardly tapered saw-tooth pattern. That is, the outwardly tapered surfaces at each end of the coupling are themselves arranged on an outward taper from the mid point of the coupling that is not as steep as their individual outward tapers. The ends of the pipe to be joined in this coupling are provided with inwardly tapered surfaces that will match the tapered surfaces of the coupling. The tapered surfaces of the coupling and the pipe ends are coated with adhesive and then the pipe ends inserted into opposite ends of the coupling.
Because the axially extending surfaces provide some mechanical locking between the pipe ends and the coupling, this joint is not as sensitive to movement before the adhesive cures. However, the tapered surfaces required on the pipe ends cannot currently be fabricated in the field and rotation of the pipe is required to assemble the joint. Thus, this joint cannot be used as a repair means. As with other bonded joints, surface contamination must be avoided. Also, as with the tapered bell and spigot configuration, the integrity of the joint formed by this means is dependent upon the pipe ends being inserted tightly within the coupling. Therefore, problems can arise with this joint if pipe length is not carefully controlled.
A joint has also been developed to allow the formation of a "no-shave" joint. That is, the bell component can be used directly with the pipe ends to be joined and no shaving of the pipe ends is required. This joint is similar to the straight socket and spigot, except that the inner diameter of the bell is large enough for the bell to fit over the outer diameter of the pipe. Adhesive is spread on the inner wall of the bell and on the outer surfaces of the pipe end and then the pipe end is inserted into the bell component. Although this joint does not require shaving, it has many disadvantages.
For "no shave" joints to be feasible, the outer diameter of the pipe has to be carefully controlled so that it will match the inner diameter of the bell. In addition, the wall thickness of the pipe has to be carefully controlled so that a uniform cylindrical surface is presented by the outer surface of the pipe adjacent the end. However, these variables can be very difficult to control in certain manufacturing processes used in making fiberglass reinforced pipe. Therefore, pipe made by these processes cannot be joined very well with "no shave" joints.
"No shave" joints are the most sensitive to movement before the adhesive has cured. Like other bonded joints, they can fail if air is trapped in the adhesive during the joining process or if surface contamination interferes with the adhesive. Irregularities in the thickness of the pipe at the ends can also lead to joint failure because gaps can occur between the outer wall of the pipe and the inner wall of the coupling bells.
Accordingly, a joint for connecting fiberglass reinforced pipe is needed that does not require shaving of the pipe or any other surface preparation for assembly, that is not sensitive to movement of the joint before any adhesive used with the joint has cured, that does not require the use of an 0-ring to prevent leaking, that does not trap air in any adhesive used with the joint during assembly which affects performance, and that is not sensitive to surface contamination. This joint should also be reusable, be capable of being formed quickly and accurately, and be capable of use in a repair coupling configuration.